Technology Developments for FIR Bolometric Detector Focal Plane Assemblies

Dr. Ari Brown (NASA/GSFC)

A discussion of recent technology developments for far-infrared bolometric detector focal plane assemblies is provided. Some of the developments include strategies for fabricating high filling fraction background limited-transition edge sensor bolometric detectors, impedance-matched absorber coatings, a micromachined blackbody source, and the capability to fabricate indium bumps on non-planar substrates.

Near-Infrared Spectroscopic Measurements of Primary Volatiles in Comets: A Unique Window into the Early Solar System

Younas Khan (U. Missouri Saint Louis)

Comets are among the most pristine solar system objects that formed in the cold midplane regions of the protosolar nebula ~ 4.5 billion years ago. They are “fossils” that provide unique insights into the chemical, physical, and dynamical conditions present in the early solar system. Near-IR spectroscopy is a valuable tool for understanding the composition of primary volatiles (i.e., volatiles directly sublimating into the coma) in comets. However, only ~50 comets have been characterized for their primary volatile composition to date. The short-period Jupiter-family comets (JFCs) are particularly underrepresented (only 15 to date). In contrast, hundreds of comets have been sampled at optical and UV wavelengths (mainly for daughter species) leading to the emergence of taxonomic schemes at these wavelengths.

My PhD dissertation is focused on understating the chemical composition and spatial outgassing behavior of an important JFC 46P/Wirtanen. 46P/Wirtanen is among the few known hyperactive comets, and it remains a suitable target for future spacecraft missions. The comet was observed in late 2018 and early 2019 during its historical apparition using the high- resolution (R~45,000), long slit (15″), near-IR spectrograph iSHELL at the NASA Infrared Telescope Facility. These observations resulted in the first comprehensive chemical characterization of the comet in the near-IR. I will present an analysis of molecular production rates (molecules s^-1) and mixing ratios (production rates with respect to H₂O) of a set of primary volatiles including H₂O, HCN, C₂H₂, NH₃, CH₃OH, CH₄, C₂H₆, H₂CO, OCS, and HC₃N in the comet. The multiple pre-, near-, and post-perihelion measurements spanning nearly two months allowed for testing any short and long-term temporal variability in production rates and mixing ratios. Owing to iSHELL’s long-slit capabilities and the comet’s exceptionally low geocentric distance (closest approach to Earth at 0.08 au; ~30 lunar distances), spatial behavior of volatiles in the inner few hundred kilometers of the coma was analyzed which will be discussed. In general, H₂O in 46P/Wirtanen exhibited extended spatial profiles which are indicative of the presence of additional outgassing sources (e.g., icy grains/chunks) in the coma, similar to the EPOXI mission target comet 103P/Hartley 2. The chemical composition of 46P/Wirtanen will be placed in context of the comet population sampled in the near-IR to date. Overall, a comprehensive analysis of the abundances of primary volatiles in 46P/Wirtanen is an important addition to the pool of comets sampled in the near-IR, in particular to the significantly underrepresented JFCs.